Musnad Abu Ya'la al-Mawsili 153:96

Abdullah ibn Numayr al-Kufi narrated to us, Ishaq ibn Sulayman narrated to us, from Hanzalah, who said: I heard Salim say: I heard Ibn Umar say: I heard the Messenger of Allah, may Allah bless him and grant him peace, say: "If your women seek your permission to go to the mosques, then give them permission."